Who is Participating?

Right, I just did some testing on your server, and it seems to be answering (well)

There are a few things though - first, you are going to need to configure your server to receive for the domain @server2.dns2go.com (which you may have already done) -> http://support.microsoft.com/kb/268838

If you're using an SBS server then you need to configure the POP 3 connector. If not, then you will need to purchase and install a 3rd party POP3 connector (I'm not sure if there are any free connectors available). i use this one - http://www.mapilab.com/exchange/pop3_connector/.
You then need to configure the connector to connect to the POP 3 server and download the messages. It is very straightforward to configure.

Just starting the POP3 service on Exchange will allow clients to connect to your Exchange server using POP3.

You do NOT need to purchase a 3rd party connector - SBS has it built in.

So, what is it that you are actually trying to do here?

Ideally, you should not be using either the POP3 service, or the POP3 connector. The POP3 service is very insecure, and a weak alternative when you have RPC/HTTP - and the POP3 connector is a piece of junk, like all POP3 connectors, and should be avoided - instead, get mail delivered directly.

I'm a beginner and I'm trying to learn how to setup Exchange on my home office Wind23k (not SBS) lab server. I have "static IP service" from DNS2GO to direct all request sent to "server2.dns2go.com" to my server.

I'd like to be able to send and receive email via my exchange server, now I can only send email using my exchange server from this addres peter@server2.dns2go.com but I can't retrieve mail that is sent to this address. and get this error from the "Postmaster"

Unlikely, I can connect to your server. And you are still getting confused with POP - it is not involved here at all.

OWA is setup by default - RPC/HTTP needs to be configured.

If you cannot receive in normal outlook, then you will not be able to receive in OWA - they are both effectively the same things.

The problem is that your server isn't configured to receive mail for that user.

Try creating a new user with a new email address - something like experts@server2.dns2go.com - the email addresses for new users should be created automatically by the server, then send mail to that and we will see how it goes